1. Field of the Invention
The present invention relates to a method of processing a particulate material containing an inflammable component in a fluidized bed chamber.
As an example, the particulate material may be wet granules of tablet materials containing an inflammable component, such as alcohol, acetone, or another solvent, and possibly also water. When the wet granulated material is being dried and/or otherwise treated in the fluidized bed, part of the inflammable component is evaporated and mixed with the fluidizing gas, which is usually air or another oxygen containing gas. The mixture of the oxygen containing gas and the evaporated inflammable component may under certain circumstances be explosive or inflammable, so that an accidental spark caused for example by static electricity may give rise to an explosion or a fire.
2. Description of the Prior Art
It is well-known to prepare wet granules of a tablet material in a combined high speed mixer and granulator to which powdered solid components and liquid components may be added. The prepared batch of the wet granules is then transferred to a fluidized bed dryer, in which atmospheric air is used as fluidizing gas.
When the wet granules contain an inflammable liquid, such as alcohol, and the granules are transferred from the combined mixer and granulator to the fluidized bed dryer at an elevated temperature (during treatment in the combined mixer and granulator the temperature of the tablet material may increase to about 40.degree. C. or even higher), the exhaust air leaving the fluidized bed may contain such a proportion of the inflammable component that a risk of explosion or ignition may exist, especially at the beginning of the drying process before the granulated material has been sufficiently cooled down due to adiabatic evaporation of the volatile inflammable component and due to contact with the normally cool fluidizing air,
It is known to reduce or eliminate the risk of explosion by using an inert fluidizing gas, such as nitrogen or a low oxygen containing gas, in an open system in which the spent inert fluidizing gas is exhausted into the atmosphere, and in a closed system, in which the inert fluidizing gas is recirculated. However, both such known methods are rather uneconomic due to the heavy investments required for the equipment, or they may be unacceptable due to the risk of contamination.